Supporting changes for CFI toolchain features

Mostly exporting variables to Bazel, but also allowlisting a BUILD
file.

Bug: 251217226
Test: Unit tests
Change-Id: Id87015a3cd5d970700c4058ec989bb0c14c36bcb
diff --git a/cc/config/global.go b/cc/config/global.go
index 4d703e4..3eb4577 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -313,6 +313,8 @@
 		"device/",
 		"vendor/",
 	}
+
+	VersionScriptFlagPrefix = "-Wl,--version-script,"
 )
 
 // BazelCcToolchainVars generates bzl file content containing variables for
@@ -401,6 +403,8 @@
 	exportedVars.ExportString("ExperimentalCStdVersion", ExperimentalCStdVersion)
 	exportedVars.ExportString("ExperimentalCppStdVersion", ExperimentalCppStdVersion)
 
+	exportedVars.ExportString("VersionScriptFlagPrefix", VersionScriptFlagPrefix)
+
 	// Everything in these lists is a crime against abstraction and dependency tracking.
 	// Do not add anything to this list.
 	commonGlobalIncludes := []string{